1. Field of the Invention
The present invention relates to an improvement in a high-frequency oscillator having a circuit formed by a microstripline.
2. Description of the Prior Art
FIG. 5 shows an example of a conventional high-frequency oscillation circuit formed by a microstripline. A resonance means 1 such as a resonance circuit, a dielectric resonator or a stripline resonator is coupled through a capacitor 2 with the collector terminal of a transistor 3 whose base is grounded.
Such a conventional high-frequency oscillation circuit is inferior in stability due to variation in capacitance of the capacitor 2.
FIG. 6 shows another example of a known high-frequency oscillation circuit, in which a second capacitor 4 is connected between a reference potential and a point 5 connecting a capacitor 2 and the collector terminal of a transistor 3, in order to compensate stability.
The second capacitor may be connected to the reference potential between the first capacitor 2 and the collector terminal of the transistor 3, in such a manner as a second capacitor 4a shown by the phantom line in FIG. 6.
However, as shown in FIGS. 7 and 8, the conventional high-frequency oscillation circuit may be influenced by reactance components X.sub.1 and X.sub.2 (FIG. 7) or X.sub.3 to X.sub.6 (FIG. 8) on the circuit pattern formed by the microstripline, depending on the manner of connecting the second capacitor 4 or 4a to the reference potential or the position of such connection. As the result, the reactance components X.sub.1 and X.sub.2 or X.sub.3 to X.sub.6 may form a series of resonance circuit with the second capacitor 4 or 4a to cause oscillation of undesirable modes, or parallel capacitance with the second capacitor 4 or 4a is increased to stop the oscillation or reduce the oscillation frequency. Thus, it has been extremely difficult to form a high-frequency oscillator stabilized in a wide frequency range by merely providing the second capacitor 4 or 4a.